1. Field of the Invention
The present invention relates to a fuel cell apparatus that generates power using fuel gas containing hydrogen and oxidizing gas containing oxygen, and a vehicle including such a fuel cell apparatus. The present invention also relates to a power management method for a system equipped with a fuel cell unit.
2. Description of the Related Art
A known fuel cell apparatus, such as the one disclosed in Japanese Patent Application Publication No. JP08-33782, has proton-conductive solid polymer electrolyte membranes in the electrolyte layers of the fuel cells. To facilitate electrochemical reactions of the fuel cells, carbon particles carrying platinum thereon, which are catalyst, are applied to the surface of each of the solid polymer electrolyte membranes. Such catalyst will hereinafter be referred to as “Pt catalyst”.
FIG. 12 is a graph showing the relationship between the oxidization-reduction potential of Pt catalyst and the output voltage of a fuel cell unit. The oxidization-reduction potential in the graph collectively represents the electric potential where oxidization of the Pt catalyst is induced, which, for example, forms an oxide film on the Pt catalyst, and that where reduction of the oxidized catalyst is induced. The “OCV” represents the open-current voltage of a fuel cell apparatus, the output voltage where no load is connected to the fuel cell apparatus, i.e., no current is supplied from the fuel cell apparatus. As shown in the graph, the open-current voltage of the fuel cell apparatus is higher than the oxidization-reduction potential of Pt catalyst that is shown by the dotted line.
In a system equipped with such a fuel cell apparatus, the region where power generation of the fuel cell apparatus is carried out frequently switches between the low potential side and the high potential side in response to, for example, changes in the amount of power required by the system. Such frequent switching of the power generation region, however, induces reduction and oxidization on the surface of the Pt catalyst, as indicated by Formula (1) and (2) below.Pt+2H2O→Pt(OH)2+2H++2e−  (1)Pt(OH)2+2H++2e−→Pt+2H2O  (2)Repetition of such oxidation and reduction causes sintering of Pt catalyst which leads to reduced power generation performance of the fuel cell apparatus.